Given the size of the Universe, the likelihood of the existence of extraterrestrial intelligence is pretty certain, however given the size of the Universe, the likelihood that we will find any (or they find us) is almost no chance. That doesn't mean we should stop looking, just that the odds are fairly depressing.

Everything we know about what life needs to exist suggests that the presence of life is probably a relatively recent phenomenon in the Universe. The only element robust enough to foster life is carbon which can only come from the cores of stars. Stars need to explode, die off, and eject their heavy matter to make planets and then life.

The early Universe was too hot and the early Stellar Era had no heavy elements. If life does exist out there, it's probably very young life that has only arrived very recently, like ours. If life is an overwhelming statistical inevitability, we might actually be the first of our kind - the earliest life-form to be consciously aware of its own existence and develop a means of escaping its home planet. As the Universe ages and more stars recycle heavy elements, the propensity for life existing elsewhere increases. That won't happen for hundreds of millions of years, however. We might be very lonely trailblazers. This is all highly speculative.

That other life hasn't contacted us is no indication that it does not exist. Distances in space are impossibly vast and it's a bit presumptuous to assume that other life is even trying to find us in the first place (or even wants to).

Furthermore, there's the Fermi paradox: That intelligent life in the Universe has such a short interstellar window that it goes extinct before it finds anyone else. Any advanced interstellar civilization that peaks and declines - possibly in a drastic way - in the order of thousands of years would appear as a mere blip-flash event to the cosmos at large; a flare-up of radiometry and extra-solar traffic rendered too short, too small, and too insignificant by the vastness of space to be detectable by anyone. A space-faring species would need to be around for tens of millions of years before anything else might detect it. The one thing the Fermi paradox might be suggesting isn't that there is no life out there but rather that traveling and/or communicating through space is very, very hard.

I think the real problem with finding aliens is the time frame. Look, we've only been able to detect space signals (other than light) for about 50 years. That's nothing compared to Earth's timeline:

Earth formed some 4.5 billion years ago.The first simple life forms developed about 4 billion years ago.It took another 3 billion years for vertebrates to arise.Two hundred million years later the first animals emerged from the sea onto land.A hundred million years later dinosaurs appeared and dominated for yet another 150 million years.The first mammals appeared about 65 million years ago, taking 60 million years to evolve the earliest humans.The first modern humans developed about 100,000 years ago.The Iron Age started about 3000 years ago.The first high powered transmissions left Earth 75 years ago (detectable only a few tens of light years away).Two years ago astronomers spent all of 3 months looking at 82 stars for signs of life...without success.Today Farkistan erupts in outrage because we haven't found anyone else out there.

Tanukis_Parachute:so does this mean i can uninstall the little seti project app from my windows 95 computers?

If you don't look, you don't find. Of what use is a Windows 95 computer, if not for doing long, slow busy work while you use your good computer to play video games and download pron faster than you could have believed possible five years ago? We've got way too much obsolete or aging technology to junk it all safely and profitably. Might as well use it for public goods.

The SETI researchers aren't surprised by not finding anything because they are perfectly aware of the difficulties and risks of the task they have assigned themselves. Ten years, twenty years, a century, a millennium ... nobody knows how long it might take, although most of the leaders don't expect short or even medium term results but the importance of the question is enough to drive the search. The SETI searchers are well aware that aliens might not broadcast radio signals--but they assume that since at least one species has been dumb enough to do it, other species are likely to be on the same low level of development. In fact, many of the galaxy's species may not have basic cable and may spend their time on the web telling each other that they don't even have a TV.

The universe may be full of hostile monsters who destroy every semi-intelligent species they meet in order to prevent rivals from developing superior organization and power, or it may be full of hipsters who can't be bothered to talk to radio-broadcasting civilizations because we're so primitive we haven't created a sub-universe yet.

But the search goes on and as new ideas for finding signs of life and intelligence occur to researchers, they will be implemented.

At the moment we can just barely detect giant planets in tight orbits around their stars by looking for wobbles and slight regular blips of light such as are produced when you throw a quarter up into the air between a distant observer and a bonfire. We don't know how much of what we consider life to be is universal or peculiar to our world's history.

But it's worth while to think about and search for answers to questions that may take centuries to answer.

After all, we are kept quite amused with questions that took thousands of years to think up, let alone answer. Many of the mathematical puzzles set by mathematicians over the last 400 years have been answered--sometimes with answers that run to book or encyclopedia size--and many remain, generating new puzzles.

I am one of those who do not mourn the loss of a mystery. As somebody observed, there are plenty more mysteries and always will be. Solve one problem, it creates a whole set of new problems of various orders of magnitude greater or smaller than the original problem. Mysteries are unlikely to run out while our species exists in some form or other.

Simple mathematics. The odds of intelligent life forming are unknown. For intelligence to evolve on our planet for example several major extinctions had to happen first. The dinosaurs ruled the planet for millions of years and never developed intelligence. Therefore on our OWN planet intelligent life is not the norm of the planet's evolution. We have no way of guessing how intelligence evolves on other planets or even if intelligence like ours is a natural end result of evolution. A LOT of things had to happen for us to inherit this planet. For all we know we ARE cosmic accidents.

The likely hood of that accident happening billions of times as SETI proponents wish to believe is only a wishful conjecture. Intelligent life in the universe is more than likely scattered on distant outposts throughout the galaxies. The odds of any two of those intelligences coming in contact with each other are infinitesimally remote.

The best situation for humanity is to live like we are the only intelligence in the universe. No aliens are coming to share their wisdom with us, the cavalry is not coming charging over the hills, so we have to live as though we are the only spark of intelligence in the galaxy, We are it, We don't get a second chance. we need to preserve our earth, terraform other planets and spread throughout the solar system and eventually the nearby stars. Like the humans at the end of The Martian Chronicles in order to meet aliens we have to become them.

cman:How do we know that aliens use the same kind of radio technology that we do?

Electromagnetic radiation is electromagnetic radiation. We've got a pretty good handle on it, we know the entire spectrum, and we know where we should look, and where we'd be wasting our time looking for various reasons.

The problem is that we're looking for aliens that are just like us.Who says creatures on another planet are using radio? Who says they care about sending or receiving messages from us? There's been life on earth for 3.5 billion years and we're the first beings that give a sh*t about this sort of thing. Who says we'll even have the ability to understand each other in the slightest way? Modern humans have been around for 50,000 years and we can still barely communicate with our dogs, much less an alien species.